The present invention relates to a suspension system mounted on a vehicle such as an automobile, and preferably used for absorbing a vibration of the vehicle.
One generally known type of a suspension system mounted on a vehicle such as an automobile is a suspension system configured to include a shock absorber (a damping force adjustable shock absorber) capable of adjusting a damping force between a vehicle body and each wheel, and adjust (control) a damping force characteristic of the shock absorber with use of a control unit (a controller) (for example, refer to Japanese Patent Application Public Disclosure No. 2011-173503).
The suspension system discussed in Japanese Patent Application Public Disclosure No. 2011-173503 is configured to perform anti-dive control of changing the damping force characteristic to the hard side when the vehicle is braked, and change at least an extension-side damping force characteristic to the soft side if a wheel load decreases when performing the anti-dive control.
On the other hand, when the vehicle slows down (decelerate) or speeds up (accelerate), a longitudinal force (a force in a front-rear direction) is applied to a wheel of the vehicle according to the slow-down or the speed-up. More specifically, the wheel (a surface thereof in contact with the ground) is subject to a braking force (a force for stopping the wheel) when the vehicle slows down, and is subject to a driving force when the vehicle speeds up. In this case, the vehicle body of the vehicle is subject to a force generated according to, for example, a suspension geometry of this vehicle and applied between the vehicle body and the wheel based on the longitudinal force applied to the wheel. Further, when the vehicle turns a corner, a lateral force (a force in a left-right direction) is applied to a wheel of the vehicle according to the cornering. More specifically, when the vehicle turns a corner, a tire lateral force is applied to the wheel (the surface thereof in contact with the ground). In this case, the vehicle body of the vehicle is subject to a force (generally, referred to as a jack-up force) generated according to, for example, the suspension geometry of this vehicle and applied between the vehicle body and the wheel based on the lateral force applied to the wheel. Therefore, if the damping force characteristic of the shock absorber is adjusted (controlled) out of consideration of the longitudinal force and the lateral force applied to the wheel, and thus the forces applied to the vehicle body based on these longitudinal force and lateral force, this may leads to excessiveness or insufficiency of the damping force, resulting in, for example, a reduction in maneuverability (a driver's maneuvering feeling) and stability.
This drawback is raised in not only the shock absorber, but also an air suspension, a hydraulic stabilizer, and the like.